RAFT polymerisation, as described in International Patent Publication Nos. WO 98/01478, WO 99/31144 and WO 10/83569, is a polymerisation technique that exhibits characteristics associated with living polymerisation. Living polymerisation is generally considered in the art to be a form of chain polymerisation in which irreversible chain termination is substantially absent. An important feature of living polymerisation is that polymer chains will continue to grow while monomer is provided and the reaction conditions to support polymerisation are favourable. Polymers prepared by RAFT polymerisation can advantageously exhibit a well defined molecular architecture, a predetermined molecular weight and a narrow molecular weight distribution or low polydispersity.
RAFT polymerisation is believed to proceed under the control of a RAFT agent according to a mechanism which is simplistically illustrated below in Scheme 1.

Scheme 1:
Proposed mechanism for RAFT polymerisation, where M represents monomer, Pn represents polymerised monomer, and Z and R are as defined below.
With reference to Scheme 1, R represents a group that functions as a free radical leaving group under the polymerisation conditions employed and yet, as a free radical leaving group, retains the ability to reinitiate polymerisation. Z represents a group that functions to convey a suitable reactivity to the C═S moiety in the RAFT agent towards free radical addition without slowing the rate of fragmentation of the RAFT-adduct radical to the extent that polymerisation is unduly retarded.
RAFT polymerisation is one of the most versatile methods of controlled radical polymerisation at least in part because of its ability to be performed using a vast array of monomers and solvents, including aqueous solutions.
Again with reference to Scheme 1, polymers produced by RAFT polymerisation, commonly referred to as RAFT polymers, inherently comprise a covalently bound residue of the RAFT agent. The RAFT agent residue itself comprises a thiocarbonylthio group (i.e. —C(S)S—) which may, for example, be in the form of a dithioester, dithiocarbamate, trithiocarbonate, or xanthate group.
In the practical application of RAFT polymers it may be desirable to remove the thiocarbonylthio group from the polymer per se. For example, the presence of the thiocarbonylthio group can cause unwanted colour in the polymer. The thiocarbonylthio group can also degrade over time to release odorous volatile sulphur containing compounds.
Even though concern over the presence of the thiocarbonylthio groups can be largely mitigated or overcome by suitable selection of the initial RAFT agent, there has been some incentive to develop techniques for removing thiocarbonylthio groups from RAFT polymers. In some circumstances, it may be necessary or desirable to deactivate the thiocarbonylthio groups due to their reactivity or to transform the groups for use in subsequent processing.
The batch wise treatment of RAFT polymer with various reagents such as nucleophiles, ionic reducing agents, oxidising agents, or treatments such as thermolysis and irradiation has been shown to remove thiocarbonylthio groups. For example, in combination with a free radical initiator, hypophosphite compounds have been shown to desulphurise RAFT polymer through radical induced reduction of the thiocarbonylthio groups. Nucleophiles such as amines have also been shown to convert thiocarbonylthio groups into thiol groups.
However such techniques can be prone to relatively poor process control and reaction uniformity leading to deficiencies in the resulting modified polymer quality. Accordingly, there remains an opportunity to develop an effective and efficient process for removing thiocarbonylthio groups from RAFT polymers, or to at least to develop a useful alternative process to those currently known.